An X-ray calibration dummy, a method for non-marker-based registration for use in navigation-guided operations employing said X-ray calibration dummy, and a medical system having such an X-ray calibration dummy.
The invention concerns an X-ray calibration dummy having markings. The invention also concerns a method for non-marker-based registration for use in navigation-guided operations employing said X-ray calibration dummy, and a medical system having such an X-ray calibration dummy.
Navigation, which is defined as guiding a medical instrument relative to a living being or relative to that portion of the tissues of said living being receiving treatment with the aid of optical imaging information, where an image of the instrument is inserted into, for example, a 2D-image or 3D-image of the living being involved obtained using an X-ray machine, is increasingly being used to support medical procedures on living beings. This approach allows an operator to guide an instrument that has at least partially penetrated the living being and whose tip is no longer directly visible due to, for example, its having penetrated bodily tissues, based on imaging information relating to that portion of the tissues of the living being that is to be treated, without running the risk of inadvertently injuring the living being.
In order to make such navigation-guided operations possible, i.e., in order to be able to insert an accurately positioned and accurately oriented image of the instrument into imaging information on a living being, a mathematical relation in the form of a coordinate transformation between a coordinate system of the imaging information on the living being or a coordinate system of the reconstructed volume of the living being and a coordinate system used for stating the positions of the instrument to be navigated will have be generated. To this end, artificial markings are occasionally arranged on the living being or anatomical markings, e.g., prominent bone structures, are established. In this case, the anatomical or artificial markings must be clearly visible on X-ray images of the living being and readily accessible on the living being. The artificial markings are, e.g., attached to the surface of the skin of the living being, in order to allow what is known as their registration, which is defined as determining the rule for transforming the spatial coordinates defined for the coordinate system used for stating the positions of the instrument to be navigated into those of the coordinate system of the imaging information on the living being or the reconstructed volume of the living being to be employed for the navigation. The markings will usually have to be individually accessed by the instrument if the coordinate transformation between the pair of coordinate systems is to be determined. The markings are also rigidly attached to the living being""s body in cases where high-precision medical procedures are involved. Examples that may be mentioned include attaching a stereotactile framework to a patient""s head or attaching markings to patients"" bones or spinal column. In some cases, the markings are attached in a separate operation, since they have to be attached prior to the preoperative medical imaging that is frequently employed for navigation purposes.
Attachment and registration of the markings is thus a rather unpleasant procedure for patients, and also relatively time-consuming for operators involved in handling preparations for navigation-guided operations.
The invention thus addresses the problem of creating the prerequisites for a simplified determination of the transformation rule applying to navigation of an instrument, particularly one that employs volumnar data. Other problems that the present invention addresses are those of stating a simplified method for determining the transformation rule without employing markers and of stating a medical system for conducting the method.
The invention solves the first problem by employing an X-ray calibration dummy that has markings that may be acquired by a position-acquisition system as a means of non-marker-based registration when performing navigation-guided operations on an object. Applying such markings to an X-ray calibration dummy creates the prerequisites for determining a transformation relationship between a coordinate system assigned to the X-ray calibration dummy and a coordinate system assigned to an X-ray system for generating the imaging to be employed for navigation purposes with the aid of a position-acquisition system under an offline procedure, for which purpose markings that may be acquired by the position-acquisition system have also been applied to the X-ray system. The X-ray calibration dummy is arranged relative to the X-ray system such that the position and orientation of the coordinate system of the X-ray calibration dummy at least largely coincide with those of the coordinate system of a volume to be reconstructed of a first object employing the X-ray system, or whose position and orientation relative to the coordinate system of the volume to be reconstructed are known. This implies that if the X-ray calibration dummy has been removed and, in general, the positions of the X-ray system and the position-acquisition system relative to one another have been altered in conjunction with the conduct of measurements on an object in comparison to their positions under the offline procedure, the relationship for transforming the coordinate system of the volume to be constructed into a coordinate system of the position-acquisition system may be determined by employing the relationship governing transformation between the coordinate system of the X-ray system and the coordinate system of the volume to be reconstructed and by acquiring the new position of the X-ray system using the position-acquisition system. If the position of a second object to be navigated relative to the first object is then also determined employing the position-acquisition system, then an image of the second object may be inserted into a volume of the first object, which volume has been reconstructed employing measurements on the first object employing the X-ray system, based on the relationship governing the transformations between the coordinate system of the position-acquisition system and the coordinate system of the volume to be reconstructed that has been determined. This implies that the X-ray calibration dummy according to the invention creates the prerequisites for simplifying determination of the rule governing transformation for navigating a second object relative to a first object, while avoiding registration involving markers.
The X-ray calibration dummy of the invention also has additional markings that will appear on X-ray images for determining offline the projection geometries of an X-ray system that may be reproducibly rotated about an axis for the purpose of reconstructing a volumnar record from a series of 2D-projections recorded at various projection angles using the X-ray system. This implies that both the transformation rules needed for navigation and the projection geometries for an X-ray system, i.e., the positions of the X-ray source and the X-ray detector, along with the projection angles and orientations of said X-ray system for every 2D-projection of a series of 2D-projections, knowledge of which is required for reconstructing a volumnar record, may be simultaneously determined under an offline procedure, i.e., prior to conducting any measurements on an object or a patient, with the aid of the X-ray calibration dummy. This in turn implies that, assuming that a suitable X-ray machine is used, for example, an X-ray machine configured in the form of a C-shaped arc, it will create the prerequisites needed for carrying out navigation based on volumnar data generated intraoperatively, without the need for employing any registrations based on markers.
The markings that may be acquired by a position-acquisition system will be arranged within a first zone of the X-ray calibration dummy and the markings that will appear on X-ray images will be arranged within a second zone of the X-ray calibration dummy that differs from the first zone of the X-ray calibration dummy, such that the determination of the transformation rules needed for the navigation will not be adversely affected by the markings that will appear on X-ray images and the determination of the projection geometries will not be adversely affected by the markings that may be acquired by the position-acquisition system.
According to one embodiment of the invention, the X-ray calibration dummy has a cylindrical shape, the first zone being one of the ends of the cylindrically shaped X-ray calibration dummy and the second zone being the lateral surface of same. According to one variant of the invention, the markings that may be acquired by the position-acquisition system are arranged on at last one marker plate attached to the X-ray calibration dummy, which marker plate is usually part of the position-acquisition system.
Another variant of the invention provides for the markings on the X-ray calibration dummy that will appear on X-ray images to be arranged in the form of a helix. Arranging the markings in the form of a helix has proven beneficial in conjunction with determining the projection geometries in the sense that only relatively few overlappings of the markings of the first zone occur on the 2D-projections for determining the projection geometries.
An X-ray calibration dummy that has a helical arrangement of markings that will appear on X-ray images for determining projection geometries is also known from U.S. Pat. No. 5,442,674.
The second problem addressed by the invention is solved by a method of non-marker-based registration for use in navigation-guided operations employing a position-acquisition system, an X-ray machine and an X-ray calibration dummy, the X-ray machine and the X-ray calibration dummy being provided with markings that may be acquired by the position-acquisition system, having the following method steps:
a) orienting the X-ray machine and the X-ray calibration dummy relative to one another such that a coordinate system assigned to the X-ray calibration dummy at least largely coincides with a coordinate system of a volume to be reconstructed of a first object, where the first object is to be X-rayed by the X-ray machine in a subsequent measurement on the first object, or such that the positions of the coordinate systems relative to one another is either known or may be determined in a simple manner,
b) determining the position and orientation of the coordinate system of the X-ray calibration dummy or of the volume to be reconstructed and of a coordinate system assigned to the X-ray machine with the position-acquisition system, and
c) determining the transformation relationship between the coordinate system of the X-ray machine and the coordinate system of the X-ray calibration dummy or the volume to be reconstructed.
As already mentioned above, if, in conjunction with measurement on an object, the X-ray calibration dummy is removed and the positions of the X-ray machine and the position-acquisition system relative to one another have changed compared to their positions during the offline procedure, the transformation relationship between the coordinate system of the volume to be reconstructed or the coordinate system of the reconstructed volume and a coordinate system of the position-acquisition system may be determined by employing the transformation relationship between the coordinate system of the X-ray system and the coordinate system of the volume reconstructed employing the X-ray machine that has been determined and by acquiring the new position of the X-ray system employing the position-acquisition system.
If finally, according to one variant of the invention, the position of a second object, e.g., an instrument, to be navigated relative to the first object is also acquired employing the position-acquisition system, the transformation relationship between the coordinate system of the position-acquisition system and the coordinate system of the volume to be reconstructed that has been determined following measurement on an object will allow an image of the instrument to be inserted into a volume that has been reconstructed employing the X-ray machine.
One embodiment of the invention provides for the first object to be positioned on a positioning mechanism that is provided with markings that may be acquired by the position-acquisition system, the position of the positioning mechanism being acquired employing the position-acquisition system and a transformation relationship between a coordinate system assigned to the positioning mechanism and the coordinate system of the X-ray calibration dummy or the coordinate system of the volume to be reconstructed is determined. This embodiment of the invention will be beneficial if the X-ray machine is removed from the positioning mechanism during the navigation-guided operation and there is the risk of the position of the position-acquisition system changing relative to the reconstructed volume due to, for example, an unintentional shift. In this case, the positioning mechanism provided with the markings will form a fixed point that may be employed for generating a relation between the coordinate system of the position-acquisition system and the coordinate system of the reconstructed volume.
Another variant of the invention provides for the first object to be provided with markings that may be acquired by the position-acquisition system during the navigation-guided operation. This will be of benefit if there is the risk of the position of the first object on the positioning mechanism changing. There would then no longer be a fixed point that would allow the determination of a transformation relationship between the coordinate system of the position-acquisition system and the coordinate system of the volume to be reconstructed or that has already been reconstructed following removal of the X-ray machine from the positioning mechanism and a shift in the position of the position-acquisition system. If, however, markings that may be acquired by the position-acquisition system are arranged on the first object itself, then a transformation relationship between a coordinate system assigned to the first object and the coordinate system of the volume to be reconstructed of the first object may be determined. This implies that, by determining the position of the first object, a transformation relationship between the position-acquisition system and the coordinate system of the volume to be reconstructed or that has already been reconstructed may be determined based on the transformation relationship between the coordinate system of the first object and the coordinate system of the volume to be reconstructed or that has already been reconstructed of the first object that has been determined, even following a change in the position of the first object.
One variant of the invention provides that, in addition to the markings that may be acquired by the position-acquisition system, the X-ray calibration dummy also has markings that will appear on X-ray images, in order that the projection geometries of the X-ray machine to be employed for reconstructing a volumnar record of the first object from recorded 2D-projections of the first object may be determined simultaneously with the determination of the transformation relationships under the offline procedure. This creates the prerequisites for carrying out navigation without registration involving markers, based on intra-operatively generated volumnar data.
The third problem addressed by the invention is solved by way of a medical system having a position-acquisition system, an X-ray machine and an X-ray calibration dummy, the X-ray machine and the X-ray calibration dummy being provided with markings that may be acquired by the position-acquisition system, it being possible for the X-ray machine and the X-ray calibration dummy also to be oriented relative to one another in a calibration procedure such that a transformation relationship between a coordinate system inscribed on the X-ray calibration dummy or a coordinate system of a volume to be reconstructed of an object to be subsequently X-rayed in conjunction with measurements on the object employing the X-ray machine and a coordinate system assigned to the X-ray machine may be determined with the aid of the position-acquisition system. Said medical system allows both determining of transformation relationships as described above and navigating of an object relative to a volume to be reconstructed.
One variant of the invention provides for the medical system to also have a positioning mechanism that has markings that may be acquired by the position-acquisition system for positioning an object to be examined. As has also been mentioned above, this approach makes it possible to determine a transformation relationship between the coordinate system of the reconstructed volume and the coordinate system of the position-acquisition system in the event that the X-ray machine is removed from the positioning mechanism and the position-acquisition system is unintentionally shifted, for example, during an operation on a patient, if the transformation relationship between the coordinate system of the positioning mechanism and the coordinate system of the volume to be reconstructed has been previously determined.